System and method for increasing the service life and/or catalytic activity of an scr catalyst and control of multiple emissions

ABSTRACT

The present invention relates generally to the field of emission control equipment for boilers, heaters, kilns, or other flue gas-, or combustion gas-, generating devices (e.g., those located at power plants, processing plants, etc.) and, in particular to a new and useful method and apparatus for reducing or preventing the poisoning and/or contamination of an SCR catalyst. In another embodiment, the method and apparatus of the present invention is designed to protect the SCR catalyst. In still another embodiment, the present invention relates to a method and apparatus for increasing the service life and/or catalytic activity of an SCR catalyst while simultaneously controlling various emissions.

RELATED APPLICATION DATA

This patent application claims priority to and is a continuation-in-partof U.S. patent application Ser. No. 12/691,527 filed Jan. 21, 2010 andtitled “System and Method for Protection of SCR Catalyst and Control ofMultiple Emissions,” which itself claims priority to and is anon-provisional of U.S. Provisional Patent Application No. 61/171,619filed Apr. 22, 2009 and titled “System and Method for Protection of SCRCatalyst.” The complete texts of these patent applications are herebyincorporated by reference as though fully set forth herein in theirentireties.

FIELD AND BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to the field of emission controlequipment for boilers, heaters, kilns, or other flue gas-, or combustiongas-, generating devices (e.g., those located at power plants,processing plants, etc.) and, in particular to a new and useful methodand apparatus for reducing or preventing the poisoning and/orcontamination of an SCR catalyst. In another embodiment, the method andapparatus of the present invention is designed to protect the SCRcatalyst. In still another embodiment, the present invention relates toa method and apparatus for increasing the service life and/or catalyticactivity of an SCR catalyst while simultaneously controlling variousemissions.

2. Description of the Related Art

NO_(x) refers to the cumulative emissions of nitric oxide (NO), nitrogendioxide (NO₂) and trace quantities of other nitrogen oxide speciesgenerated during combustion. Combustion of any fossil fuel generatessome level of NO_(x) due to high temperatures and the availability ofoxygen and nitrogen from both the air and fuel. NO_(x) emissions may becontrolled using low NO combustion technology and post-combustiontechniques. One such post-combustion technique involves selectivecatalytic reduction (SCR) systems in which a catalyst facilitates achemical reaction between NO and a reagent (usually ammonia) to producemolecular nitrogen and water vapor.

SCR technology is used worldwide to control NO emissions from combustionsources. This technology has been used widely in Japan for NO controlfrom utility boilers since the late 1970's, in Germany since the late1980's, and in the US since the 1990's. Industrial scale SCRs have beendesigned to operate principally in the temperature range of 500° F. to900° F., but most often in the range of 550° F. to 750° F. SCRs aretypically designed to meet a specified NO reduction efficiency at amaximum allowable ammonia slip. Ammonia slip is the concentration,expressed in parts per million by volume, of unreacted ammonia exitingthe SCR.

For additional details concerning NO removal technologies used in theindustrial and power generation industries, the reader is referred toSteam/its generation and use, 41^(st) Edition, Kitto and Stultz, Eds.,Copyright 2005, The Babcock & Wilcox Company, Barberton, Ohio, U.S.A.,particularly Chapter 34—Nitrogen Oxides Control, the text of which ishereby incorporated by reference as though fully set forth herein.

Regulations issued by the EPA promise to increase the portion of utilityboilers equipped with SCRs. SCRs are generally designed for a maximumefficiency of about 90%. This limit is not set by any theoretical limitson the capability of SCRs to achieve higher levels of NO destruction.Rather, it is a practical limit set to prevent excessive levels ofammonia slip. This problem is explained as follows.

In an SCR, ammonia reacts with NO according to one or more of thefollowing stoichiometric reactions (a) to (d):

4NO+4NH₃+O₂→4N₂+6H₂O  (a)

12NO₂+12NH₃→12N₂+18H₂O+3O₂  (b)

2NO₂+4NH₃+O₂→3N₂+6H₂O  (c)

NO+NO₂+2NH₃→2N₂+3H₂O  (d).

The above catalysis reactions occur using a suitable catalyst. Suitablecatalysts are discussed in, for example, U.S. Pat. Nos. 5,540,897;5,567,394; and 5,585,081 to Chu et al., all of which are herebyincorporated by reference as though fully set forth herein. Catalystformulations generally fall into one of three categories: base metal,zeolite and precious metal.

Base metal catalysts use titanium oxide with small amounts of vanadium,molybdenum, tungsten or a combination of several other active chemicalagents. The base metal catalysts are selective and operate in thespecified temperature range. The major drawback of the base metalcatalyst is its potential to oxidize SO₂ to SO₃; the degree of oxidationvaries based on catalyst chemical formulation. The quantities of SO₃which are formed can react with the ammonia carryover to form variousammonium-sulfate salts.

Zeolite catalysts are aluminosilicate materials which function similarlyto base metal catalysts. One potential advantage of zeolite catalysts istheir higher operating temperature of about 970° F. (521° C.). Thesecatalysts can also oxidize SO₂ to SO₃ and must be carefully matched tothe flue gas conditions.

Precious metal catalysts are generally manufactured from platinum andrhodium. Precious metal catalysts also require careful consideration offlue gas constituents and operating temperatures. While effective inreducing NO_(N), these catalysts can also act as oxidizing catalysts,converting CO to CO₂ under proper temperature conditions. However, SO₂oxidation to SO₃ and high material costs often make precious metalcatalysts less attractive.

As is known to those of skill in the art, various SCR catalysts undergopoisoning when they become contaminated by various compounds including,but not limited to, certain phosphorus compounds such as phosphorusoxide (PO) or phosphorus pentoxide (P₂O₅). Additionally, it is also wellknown that SCR catalysts degrade over time and have to be replacedperiodically at a significant cost and loss of generating capacity. In atypical 100 MWe coal plant the downtime and cost associated with thereplacement of underperforming catalyst can be in the neighborhood ofone million US dollars or more.

More particularly, as the SCR catalysts are exposed to the dust ladenflue gas there are numerous mechanisms including blinding, masking andpoisoning that deactivates the catalyst and causes a decrease in thecatalyst's performance over time. The most common catalyst poisonencountered when burning eastern domestic coal (i.e., coal mined in theeastern United States) is arsenic. The most common catalyst poisonencountered when burning western domestic coal (i.e., coal mined in thewestern United States) is phosphorus and calcium sulfate is the mostcommon masking mechanism. One method of recycling the used catalyst isthe process called regeneration washing or rejuvenation. The initialsteps of the regeneration process involve the removal of these toxicchemicals by processing the catalysts through various chemical baths inwhich the poisons are soluble. While this treatment process does anexcellent job of removing the desired poisons it produces wastewaterwith very high arsenic concentrations.

In another situation, Powder River Basin/Lignite coal plants, anycoal/biomass co-combustion, or any coal/bone meal co-combustion or evenpure biomass combustion power plants will suffer from phosphoruscontamination of their SCR catalysts.

Additionally, beyond controlling NO_(N) emissions, other emissioncontrols must be considered and/or met in order to comply with variousstate, EPA and/or Clean Air Act regulations. Some other emissioncontrols which need to be considered for boilers, heaters, kilns, orother flue gas-, or combustion gas-, generating devices (e.g., thoselocated at power plants, processing plants, etc.) include, but are notlimited to, mercury, SO_(N), and certain particulates.

Given the above, a need exists for a method that provides for anyeconomical and environmentally suitable method and/or system to increasecatalytic life span and/or catalytic activity of an SCR catalyst whilepermitting, in some instances, the simultaneous removal of variousgaseous compounds (e.g., phosphorus or mercury) from a combustionprocess.

SUMMARY OF THE INVENTION

The present invention relates generally to the field of emission controlequipment for boilers, heaters, kilns, or other flue gas-, or combustiongas-, generating devices (e.g., those located at power plants,processing plants, etc.) and, in particular to a new and useful methodand apparatus for reducing or preventing the poisoning and/orcontamination of an SCR catalyst. In another embodiment, the method andapparatus of the present invention is designed to protect the SCRcatalyst. In still another embodiment, the present invention relates toa method and apparatus for increasing the service life and/or catalyticactivity of an SCR catalyst while simultaneously controlling variousemissions.

Accordingly, one aspect of the present invention is drawn to a methodfor increasing the active life of an SCR catalyst, the method comprisingthe steps of: (a) providing at least one iron-bearing compound to acombustion zone or flue gas stream of a furnace, or boiler, prior toentry of the flue gas into an SCR; (b) permitting the at least oneiron-bearing compound to react with any gaseous phosphorus compounds, orphosphorus-containing compounds, present in the combustion zone or fluegas prior to the entry of the flue gas into the SCR; (c) providing atleast one halide-bearing compound to a combustion zone or flue gasstream of a furnace, or boiler, prior to entry of the flue gas into anSCR, with the proviso that halide-bearing compound is not an ironhalide; and (d) permitting the at least one halide-bearing compound toreact with and/or oxidize any mercury present in the combustion zone orflue gas, wherein the method achieves an increase in either one, orboth, of a catalytic activity and/or a catalytic lifespan of at leastabout 10 percent at an operational time of at least about 2,000 hours.

In yet another aspect of the present invention, there is provided amethod for increasing the active life of an SCR catalyst, the methodcomprising the steps of: (i) providing at least one iron-bearingcompound to a combustion zone or flue gas stream of a furnace, orboiler, prior to entry of the flue gas into an SCR; (ii) permitting theat least one iron-bearing compound to react with any gaseous phosphoruscompounds, or phosphorus-containing compounds, present in the combustionzone or flue gas prior to the entry of the flue gas into the SCR; (Iii)providing at least one halide-bearing compound to a combustion zone orflue gas stream of a furnace, or boiler, prior to entry of the flue gasinto an SCR, with the proviso that halide-bearing compound is not aniron halide; and (iv) permitting the at least one halide-bearingcompound to react with and/or oxidize any mercury present in thecombustion zone or flue gas, wherein the method achieves an increase ineither one, or both, of a catalytic activity and/or a catalytic lifespanof at least about 10 percent at an operational time of at least about3,000 hours.

In yet another aspect of the present invention, there is provided amethod for simultaneously sequestering one or more phosphorus compounds,or phosphorus-containing compounds, in the form of one or more lessreactive iron-phosphorus-containing compounds, and oxidizing mercury,the method comprising the steps of: (A) providing at least oneiron-bearing compound to a combustion zone or flue gas stream of afurnace, or boiler; (B) permitting the at least one iron-bearingcompound to react with any gaseous phosphorus compounds, orphosphorus-containing compounds, present in the combustion zone or fluegas to form one or more less reactive iron-phosphorus-containingcompounds; (C) providing at least one halide-bearing compound to acombustion zone or flue gas stream of a furnace, or boiler, prior toentry of the flue gas into an SCR, with the proviso that halide-bearingcompound is not an iron halide; and (D) permitting the at least onehalide-bearing compound to react with and/or oxidize any mercury presentin the combustion zone or flue gas, wherein the method achieves anincrease in either one, or both, of a catalytic activity and/or acatalytic lifespan of at least about 10 percent at an operational timeof at least about 4,000 hours.

In yet another aspect of the present invention, there is provided amethod for simultaneously sequestering one or more phosphorus compounds,or phosphorus-containing compounds, in the form of one or more lessreactive iron-phosphorus-containing compounds, and oxidizing mercury,the method comprising the steps of: (I) providing at least oneiron-bearing compound to a combustion zone or flue gas stream of afurnace, or boiler; (II) permitting the at least one iron-bearingcompound to react with any gaseous phosphorus compounds, orphosphorus-containing compounds, present in the combustion zone or fluegas to form one or more less reactive iron-phosphorus-containingcompounds; (III) providing at least one halide-bearing compound to acombustion zone or flue gas stream of a furnace, or boiler, prior toentry of the flue gas into an SCR, with the proviso that halide-bearingcompound is not an iron halide; and (IV) permitting the at least onehalide-bearing compound to react with and/or oxidize any mercury presentin the combustion zone or flue gas, wherein the method achieves anincrease in either one, or both, of a catalytic activity and/or acatalytic lifespan of at least about 15 percent at an operational timeof at least about 3,000 hours.

In yet another aspect of the present invention, there is provided amethod for sequestering one or more phosphorus compounds, orphosphorus-containing compounds, in the form of one or more lessreactive iron-phosphorus-containing compounds while concurrentlysequestering mercury, the method comprising the steps of: providing atleast one iron-bearing compound to a combustion zone or flue gas streamof a furnace, or boiler; permitting the at least one iron-bearingcompound to react with any gaseous phosphorus compounds, orphosphorus-containing compounds, present in the combustion zone or fluegas to form one or more less reactive iron-phosphorus-containingcompounds; providing at least one halide-bearing compound to acombustion zone or flue gas stream of a furnace, or boiler, prior toentry of the flue gas into an SCR, with the proviso that halide-bearingcompound is not an iron halide; and permitting the at least onehalide-bearing compound to react with and/or oxidize any mercury presentin the combustion zone or flue gas, wherein the method achieves anincrease in either one, or both, of a catalytic activity and/or acatalytic lifespan of at least about 15 percent at an operational timeof at least about 4,000 hours.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this disclosure. For a better understanding of the invention,its operating advantages and specific benefits attained by its uses,reference is made to the accompanying drawings and descriptive matter inwhich exemplary embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a typical fossil fuel burningfacility with an SCR system, and which includes a system for practicingthe methods of the present invention; and

FIG. 2 is a graph illustrating one example of an increase in catalyticactivity and catalytic lifespan as realized via utilization of a systemand method in accordance with one embodiment of the present invention.

DESCRIPTION OF THE INVENTION

While the present invention will be described in terms of SCR systemswhich use ammonia as the NO_(N) reducing agent, since ammonia isfrequently preferred for economic reasons, the present invention is notlimited to ammonia based systems. The concepts of the present inventioncan be used in any system which uses an ammoniacal compound. As used inthe present disclosure, an ammoniacal compound is a term meant toinclude compounds such as urea, ammonium sulfate, cyanuric acid, andorganic amines as well as ammonia (NH₃). These compounds could be usedas reducing agents in addition to ammonia, but as mentioned above,ammonia is frequently preferred for economic reasons. Somenon-ammoniacal compounds such as carbon monoxide or methane can be usedas well, but with loss in effectiveness.

Although the present invention is described in relation to a boiler, ora fossil fuel boiler, it is not limited solely thereto. Instead, thepresent invention can be applied to any combustion source that generatesNO_(N) regardless of whether such a combustion source is utilized inconjunction with a boiler, or a steam generator. For example, thepresent invention could be used in combination with a kiln, a heater, orany other type of combustion process that generates, in whole or inpart, a flue gas or combustion gas containing NO_(N). Accordingly, thedescription below is to be construed as merely exemplary.

As illustrated in FIG. 1, the present invention may be applied to aboiler installation which employs a wet flue gas desulfurization (WFGDor wet scrubber) for removal of sulfur oxides from the flue gases, asshown in the upper right-hand side of FIG. 1. In this configuration, thewet scrubber is typically preceded (with respect to a direction of fluegas flow through the system) by a particulate collection device (PCD),advantageously a fabric filter (FF) bag house, or an electrostaticprecipitator (ESP). If desired, there may also be provided a wetelectrostatic precipitator (wet ESP or WESP) which may be provided as afinal “polishing” stage for fine particulate or SO₃. Alternatively, thepresent invention may be applied to a system which employs a spray dryerapparatus (SDA) or dry scrubber for removal of sulfur oxides from theflue gases, as shown in the lower right-hand side of FIG. 1. In thisconfiguration, the SDA or dry scrubber is typically followed (withrespect to a direction of flue gas flow through the system) by aparticulate collection device (PCD), advantageously a fabric filter (FF)or baghouse, an electrostatic precipitator (ESP) or even a wetelectrostatic precipitator (wet ESP).

Additionally, the present invention can be applied to any SCR catalystthat is adversely affected by poisoning with a phosphorus-based compoundsuch as, but not limited to, H₃PO₄, PO or P₂O₅. As such, the presentinvention is not limited to any one type of SCR catalyst, but rather isbroadly applicable to a wide range of SCR catalyst systems. Suitablecatalyst systems for which the present invention is applicable include,but are not limited to, honeycomb, plate or corrugated typeconfigurations.

In one embodiment, the present invention is directed to reducing therate of SCR catalyst deactivation on Powder River Basin (PRB) coalcombustion units. It should be noted that although the present inventionis described in relation to PRB coal, the present invention is notlimited thereto. Rather, the present invention is broadly applicable toany situation where an SCR catalyst is poisoned by one or more gaseousphosphorus compounds.

In one embodiment, phosphorus in PRB coal is suspected to cause rapiddeactivation in staged combustion and other units. This deactivation issuspected to be caused by the gas phase phosphorus released viacarbothermic reduction reaction. In this reaction under oxygen deficientconditions, phosphorus bearing compounds release gas phase phosphorus bythe following reaction:

P₂O₅(solid phase compounds)+3C(s)→2PO(g)+3CO(g).

This gas phase phosphorus attaches to the active sites within thecatalyst causing the deactivation of the sites for NO_(x) reduction. Asa result of this deactivation the SCR catalyst cannot carry out theNO_(x) reduction process to the same performance level as unusedcatalyst.

In one embodiment, the present invention relates to a system and methodto prevent formation of gas phase phosphorus species in the combustionenvironment thus reducing, mitigating and/or eliminating the rate of SCRdeactivation. In one embodiment, the present invention accomplishes theaforementioned goal by the addition of at least one iron-bearingcompound to the PRB coal prior to combustion.

In another embodiment, the present invention is directed to a system andmethod designed to increase the catalytic activity and/or catalytic lifespan. In this case, the increase in catalytic activity and/or increasein catalytic life span is measured against a standard, or known, rate ofdecline in catalytic activity and/or life for a given a boiler, fossilfuel boiler, kiln, heater, or any other type of device that generates aflue gas or combustion gas containing NO_(x).

In one embodiment, the iron-bearing compounds of the present inventionis any iron compound (e.g., an iron oxide compound) that is able toundergo reduction in the combustion environments common to boilers,furnaces, power plants, etc. In one particular embodiment, theiron-bearing compound is iron (III) oxide (Fe₂O₃), also known as rediron oxide or hematite. In the embodiment where iron (III) oxide isutilized the reactions of interest that occur in the combustion portionof a boiler or furnace are as shown below:

3Fe₂O₃(s)+CO(g)→2Fe₃O₄(s)+CO₂(g)  (1)

Fe₃O₄(s)+CO(g)→3FeO(s)+CO₂(g)  (2).

It should be noted that the Fe₃O₄, also known as black iron oxide ormagnetite, of the first reaction above can also be written moreaccurately as FeO.Fe₂O₃. The FeO or iron (II) oxide, also known asferrous oxide, which is generated due to the reduction of Fe₂O₃ is thenavailable to tie-up, bind and/or sequester any PO gas present in thecombustion zone, or the flue gas, of a boiler, or furnace, prior toarrival at the SCR. This PO gas will then form Fe—P compounds inparticulate phase prior to arrival at the SCR. The particulate will passthrough the catalyst and avoid the catalyst deterioration.

In another embodiment, the present invention can utilize iron (II)carbonate which is converted to the desired iron (II) oxide in thecombustion zone via the reaction shown below:

FeCO₃(s)→FeO(s)+CO₂(g)  (3).

In still another embodiment, the present invention can utilize acombination of one or more iron-containing compounds and one or morehalide compounds, with the proviso that the halide containing compoundis not an iron halide. Thus, in this embodiment at least oneiron-containing compound is utilized in conjunction with at least onenon-iron halide containing compound. In still another embodiment, the atleast one iron compound has a generic formula of AX, where A is equal toiron and X is either an oxide or carbonate ion, anion, group, and/ormoiety and the at least one halide compound has a generic formula of BYwhere B is any atom, element, or cation except for iron and Y is ahalide selected from chlorine, bromine, fluorine, or iodine.

In one embodiment, suitable halides for use in conjunction with thepresent invention include, but are not limited to, potassium bromide,potassium chloride, potassium fluoride, potassium iodide, sodiumbromide, sodium chloride, sodium fluoride, sodium iodide, calciumbromide, calcium chloride, calcium fluoride, calcium iodide, aluminumbromide, aluminum chloride, aluminum fluoride, aluminum iodide, othertransition metal halides (e.g., bromides, chlorides, fluorides and/oriodides) with the proviso that the transition metal is not iron, or anymixture of two or more thereof. In still another embodiment, any one ormore halide compounds in accordance with the proviso defined above canbe used in combination with one or more non-halide containing ironcompounds (e.g., iron (II) carbonate). In still another embodiment, thepresent invention utilizes a combination of iron (II) carbonate withcalcium bromide to control the amount of phosphorus in a flue gas, orcombustion gas while concurrently permitting both the control of mercurycompounds, or mercury-containing compounds, in a flue gas, or combustiongas and the increase in catalytic activity and/or service life. In stillyet another embodiment, the present invention utilizes a combination ofiron (II) carbonate with calcium chloride to control the amount ofphosphorus in a flue gas, or combustion gas while concurrentlypermitting both the control of mercury compounds, or mercury-containingcompounds, in a flue gas, or combustion gas and the increase incatalytic activity and/or service life. In still yet another embodiment,the present invention utilizes a combination of iron (II) carbonate witheither one, or both, of aluminum bromide and/or aluminum chloride tocontrol the amount of phosphorus in a flue gas, or combustion gas whileconcurrently permitting both the control of mercury compounds, ormercury-containing compounds, in a flue gas, or combustion gas and theincrease in catalytic activity and/or service life. As used herein,mercury compounds, or mercury-containing compounds, include, but are notlimited to, any compound that contains either oxidized mercury, or boundelemental mercury. In still another embodiment, the present invention isdirected to concurrently permitting the control of mercury compounds, ormercury-containing compounds, that contain primarily, or only, oxidizedmercury.

As used herein, any iron compound suitable for use in conjunction withthe present invention can be utilized in a hydrated or non-hydratedform. As such, reference to any iron compound herein by definitionincludes any hydrated forms that exists whether or not specificallymentioned by chemical formula.

As is known in the art, (see, e.g., United States Patent ApplicationPublication No. 2008/0107579 the text of which is hereby incorporated byreference as though fully set forth herein) halide-containing compoundsare utilized to oxidize elemental mercury present in a flue, orcombustion, gas. Due to this oxidation reaction, the halide portion of asuitable halide-containing compound permits elemental mercury to beconverted into a more favorable form for subsequent capture, orsequestration, via one or more suitable environmental controltechnologies (e.g., a wet scrubber or spray dry absorber (SDA), a fluegas desulfurization system (FGD), a powdered activated carbon system(PAC), or a particulate collecting system such as a fabric filter (FF)or a electrostatic precipitator (ESP)). In one instance, as is known inthe art, the addition of one or more suitable halide-containingcompounds also increases the amount of mercury that isparticulate-bound. Given that numerous patents and publishedapplications detail the manner by which suitable halide-containingcompounds permit the increased recovery of mercury from a flue, orcombustion, gas, a detailed discussion hereof is omitted for the sake ofbrevity.

In any of the above embodiments, the suitable one or more iron-bearingcompounds, and if so desired the one or more halide compounds, can beadded to the coal via one or more pulverizers. In still anotherembodiment, the one or more iron-bearing compounds, and if so desiredthe one or more halide compounds, of the present invention can be addedto the combustion zone of a boiler and/or furnace via one or moresuitable supply lines designed to deliver a powderized, solid, aqueoussuspension, suspension, or aqueous solution of the one or moreiron-bearing compounds and/or the one or more halide compounds to thecombustion zone of a furnace and/or boiler. To this end, FIG. 1illustrates several embodiments of suitable design schemes foraccomplishing this result.

Referring to FIG. 1, there is illustrated a schematic representation ofa typical fossil fuel burning facility, generally designated 10, with anSCR system, and which includes a system for practicing the methods ofthe present invention. As shown, boiler 12 is provided for extractingthe heat from the combustion of a fossil fuel, such as coal, throughcombustion with an oxidant, typically air. The heat is transferred to aworking fluid, such as water, to generate steam used to either generatepower via expansion through a turbine generator apparatus (not shown) orfor industrial processes and/or heating.

The raw coal 14 must be crushed to a desired fineness and dried tofacilitate combustion. Raw coal 14 is temporarily stored in a coalbunker 16 and then transferred by means of a gravimetric or volumetricfeeder 18 to one or more coal pulverizers 20. In the embodiment shown inFIG. 1, there are six (6) coal pulverizers, identified as coalpulverizers A-F. As is known to those skilled in the art, each coalpulverizer 20 grinds the coal to a desired fineness (e.g., 70% through200 mesh) and as it is ground, hot primary air from primary air fans(not shown) is conveyed into each coal pulverizer 20 to preheat andremove moisture from the coal to desired levels as it is ground. Theprimary air is also used to convey the pulverized coal (PC) out of eachcoal pulverizer 20 and delivers it along a plurality of pulverized coalsupply lines (one such burner line is identified at A in FIG. 1; asingle coal pulverizer 20 may supply coal through 4-8 pulverized coalsupply lines) to the burners 22 on the front and rear walls of theboiler 12. Typically, the burners 22 are located in spaced elevations onone or both of the opposed front and rear walls of the boiler 12, or atthe corners of the boiler in installations known as corner-fired ortangentially-fired units (not shown). The present invention can beutilized in conjunction with, but is not limited solely to, single-wallfired, opposed-wall fired and corner- or tangentially-fired units.Typically, a single coal pulverizer 20 only provides coal to a singleelevation of burners 22 on a wall. Thus, in the embodiment shown in FIG.1, the six coal pulverizers A-F supply corresponding burner elevationsA-F. However, as is known to those skilled in the art, other pulverizerand burner configurations are known (e.g., single pulverizers supplyingburners on multiple walls and/or elevations or multiple pulverizerssupplying burners on a single elevation) and the present inventionapplies to any such configurations.

The combustion process begins in the burner zone 24 of the boiler 12'sfurnace 26, releasing heat and creating hot flue gas 28 which isconveyed upwardly to the upper portion 30 of the boiler 12, acrossheating surfaces schematically indicated as rectangles 32. The flue gas28 is then conveyed across the heating surfaces in the pendantconvection pass 34, into the upper portion 36 of the horizontalconvection pass 38. The flue gas 28 is then conveyed through a selectivecatalytic reduction (SCR) apparatus 40 where NO_(x) in the flue gas isreduced, and then through primary and secondary air heater devicesschematically indicated at 42. The air heaters 42 extract additionalheat from the flue gas 28, lowering the temperature of the flue gas, andpreheat the incoming air used for combustion.

As illustrated in FIG. 1, and downstream of the air heaters 42, the fluegas 28 undergoes further treatment for the removal of particulates andsulfur oxides. Two typical configurations of the downstream equipmentemployed to accomplish these tasks are shown on the right-hand side ofFIG. 1. The upper equipment configuration in FIG. 1 comprises aparticulate collection device (PCD) schematically indicated at 44, forremoval of particulates from the flue gas 28, and which may comprise inpractice a fabric filter or an electrostatic precipitator. Downstream ofthe PCD 44 there is provided a wet flue gas desulfurization (WFGD)device, also known as a wet scrubber, for removal of sulfur oxides fromthe flue gas 28. The cleaned, scrubbed flue gas may (optionally) beconveyed through a wet ESP 47 for removal of fine particulate or SO₃,and then conveyed to stack 48 for discharge to the atmosphere.

The lower equipment configuration in FIG. 1 comprises a spray dryerapparatus (SDA) schematically indicated at 50, also known as a dryscrubber, for removal of sulfur oxides from the flue gas 28. Downstreamof the SDA 50 there is provided a particulate collection device (PCD)44, as described above, for removal of particulates from the flue gas28. The cleaned, scrubbed flue gas is then conveyed to stack 48 fordischarge to the atmosphere.

In order to further reduce NO_(x) emissions, some boilers 12 employstaged combustion wherein only part of the stoichiometric amount of airis provided in the main burner zone 24, with the balance of the air forcombustion, together with any excess air required due to the fact thatno combustion process is 100% efficient, is provided above the burnerzone 24 via over fire air (OFA) ports 52. If staged combustion isemployed in a boiler 12, due to the reduced air supplied to the burnerzone 24, a reducing atmosphere is created in the lower portion of thefurnace 26, including the hopper region 54.

In accordance with a first embodiment of the present invention, one ormore suitable iron-bearing compounds, and if so desired one or moresuitable halide compounds, are added to the one or more coal pulverizers20 prior to supplying the pulverized coal to the one or more burners 22.The system and apparatus for accomplishing this desired result is alsoshown in FIG. 1, generally designated 100. The system 100 comprises astorage means 120 for temporarily storing the iron-based phosphorusreduction compound, and if so desired the mercury reducing compound,generally designated 110; delivery means 130, 135 for conveying thecompound 110 to a desired location, including valves, seals, etc. asrequired; and control means 150, advantageously microprocessor-basedcontrol means, which are accessed via an operator via human operatorinterface (I/O) station 160, which includes display and data collectionand storage means as required. Although not illustrated individually,the system of the present invention can, in one embodiment, utilizeindependent storage, delivery and control means (in accordance withthose described above) for each individual iron and/or halide compound.In still another embodiment, the system of the present invention cancomprise one set of storage, delivery and control means for the ironcompounds or compounds utilized herein and one set of storage, deliveryand control means (in accordance with those described above) for thehalide compound or compounds utilized herein.

In FIG. 1, the raw coal 14 to which the iron-based phosphorus reducingcompound 110 has been added is referred to as 140. Advantageously, theiron-based phosphorus reducing compound 110 may be provided along withthe raw coal 14 via the feeder 18, which permits close control andmeasurement of the delivery of both raw coal 14 and iron-basedphosphorus reducing compound 110 into the coal pulverizer 20.Alternatively, the iron-based phosphorus reducing compound 110 may beprovided directly into the coal pulverizer 20 and/or directly into oneor more individual burner lines A-F providing the pulverized coal toindividual burners 22, with suitable sealing devices against thepositive pressure within the coal pulverizer 20 or burner lines A-F. Thedelivery means may be slurry-based or pneumatic as required by theparticulars of the iron-based phosphorus reducing compound 110 and theamount and location of introduction into the flue gas 28. Aninterconnected arrangement of control or signal lines 170, 180, 190 and195 interconnect these various devices to provide control signals,iron-based phosphorus reducing compound 110 level signals, andphosphorus level signals in the flue gas 28 (from a sensor 200) topermit the introduction of the iron-based phosphorus reducing compound110 into the flue gas 28 to be controlled by a human operator, orautomatically controlled. However, if a suitable, real-time sensor 200for measuring levels of gaseous phosphorus in the flue gas 28 is notavailable, flue gas samples may instead be taken at the location 200 forlater laboratory analysis via suitable test methods, which may beinductively coupled plasma—mass spectrometry (ICP-MS). Based upon thelaboratory results, a human operator could then use the operatorinterface 160 to manually input a desired set-point into control means150 for the amount of iron-based phosphorus reducing compound 110introduced into the flue gas 28. Provided that subsequent laboratoryanalyses do not indicate any significant variation in gaseous phosphoruslevels in the flue gas 28, there may be no need for real-time, closecontrol of the introduction of iron-based phosphorus reducing compound110. Instead, the amount of iron-based phosphorus reducing compound 110introduced into the flue gas 28 may be simply a function of boiler loador coal feed rate values.

In still yet another embodiment, the present invention utilizes iron(II) oxide. In this embodiment, the need for a reduction reaction tooccur is eliminated and the addition points for the iron (II) oxide ofthis embodiment are therefore broader then previous embodiments. In thiscase, the iron (II) oxide can be added at any suitable pointpost-combustion and pre-SCR in order to tie up, bind and/or sequesterany PO gas present in the flue gas of a boiler, or furnace, prior toarrival at the SCR. In particular, the iron-based phosphorus reductioncompound can be supplied at one or more of the locations G through Qshown in FIG. 1. More particularly, the iron-based phosphorus reductioncompound can also be provided into the flue gas 28 at one or more of thefollowing locations:

-   -   G: into or below the burner zone 24, in one or more of the        front, rear or side walls, via means separate from the burners        22;    -   H: into the furnace 26 at a location above the burner zone 24,        in one or more of the front, rear or side walls;    -   I, J: into the furnace 26 in the vicinity of or via the OFA        ports 52 on one or both of the front or rear walls;    -   K: into the boiler 12 in the pendant convection pass 34;    -   L: into the boiler 12 in the upper portion 36 of the horizontal        convection pass 38;    -   M, N, O, P: into the boiler 12 in the horizontal convection pass        38; and/or    -   Q: into the boiler 12 in the hopper region below the horizontal        convection pass 38.

Given the above, it should be noted that in addition to the introductionof the one or more iron-based phosphorus reduction compounds, theabove-mentioned systems, methods and/or control apparatuses and/ortechnologies can also be utilized to introduce one or more halidecompounds in accordance with the present invention as detailed above.Thus, in one embodiment, the present invention is directed to a systemwhereby both one or more iron-based compounds and one or more halidecompounds are supplied in any manner per the various methods and/orsystems described herein. In another embodiment, each type of compound,or even each separate compound regardless of type, can be suppliedindividually. In still another embodiment, any combination of two ormore compounds regardless of type (i.e., whether an iron-based compoundor a halide compound) can be supplied together so long as the onecompound does not react detrimentally with the other compound.

Furthermore, given the above, the reduced iron, or iron (II) oxide, ofthe present invention is able to remove the gas phase phosphorus in theform of iron-phosphorus alloys which upon coming in contact with theover fire air from iron-phosphorus oxide compounds. This significantlyreduces the amount of gas phase phosphorus accumulation in an SCRcatalyst. Another advantage of the present invention is that throughaddition of iron a significant portion of any phosphorus present will beiron-bound. Iron-bound phosphorus compounds are less leachable therebyminimizing the transfer of phosphorus to an SCR catalyst. Furthermore,phosphorus associated with and/or bound to an iron compound (e.g., aniron oxide) is more stable than phosphorus that is associated withand/or bound to a calcium compound (e.g., calcium oxide). Given this,the present invention is, in one embodiment, directed to the situationwhere a majority of the phosphorus present in the combustion and/or fluestream is sequestered in a suitable iron-phosphorus-oxygen-containingcompound thereby substantially reducing the amount ofcalcium/phosphorus/oxygen-containing compounds that are able to reactwith SO_(x). This in turn substantially reduces the amount of gaseousphosphorus that is produced in the combustion and/or flue gas stream byrestricting the amount of calcium/phosphorus/oxygen-containing compoundsthat are present in the combustion and/or flue gas stream to react withvarious SO_(X) compounds resulting in the unwanted production of gaseousphosphorus compounds, or phosphorus/oxygen compounds, that can lead tothe undesired poisoning of an SCR catalyst.

In still another embodiment, the iron-bearing compounds and/or halidecompounds of the present invention can be added in any suitable manner,including the manner detailed in the FIG. 1. Suitable iron-bearingcompounds include, but are not limited to, aqueous and soluble forms ofiron-bearing compounds such as metallic iron, one or more iron oxides,iron carbonate, or mixtures of two or more thereof. Suitable halidecompounds include, but are not limited to, potassium bromide, potassiumchloride, potassium fluoride, potassium iodide, sodium bromide, sodiumchloride, sodium fluoride, sodium iodide, calcium bromide, calciumchloride, calcium fluoride, calcium iodide, aluminum bromide, aluminumchloride, aluminum fluoride, aluminum iodide, other transition metalhalides (e.g., bromides, chlorides, fluorides and/or iodides) with theproviso that the transition metal is not iron, or any mixture of two ormore thereof. If an existing skid is used then one or more aqueousreagents can be pumped via positive displacement pumps from a storagetank to the one or more coal feeders where the reagent is sprayed on thecoal as the coal passes on a feeder belt upstream of the pulverizers. Inthis instance, if so utilized the one or more halide compounds arechosen to be soluble in water, or an aqueous-based solvent. Suitablehalides soluble halides include, but are not limited to, potassiumbromide, potassium chloride, potassium fluoride, potassium iodide,sodium bromide, sodium chloride, sodium fluoride, sodium iodide, calciumbromide, calcium chloride, calcium iodide, aluminum bromide, aluminumchloride, aluminum iodide, or any mixtures of two or more thereof. Instill another embodiment, other transition metal halides (e.g.,bromides, chlorides, fluorides and/or iodides) that are not iron halidescan be utilized so long as such compounds are, in this embodiment,soluble in water, or an aqueous-based solvent.

In one embodiment, the present invention is advantageous in that it isapplicable to both existing SCRs (retrofits) and new SCRs. Additionally,the present invention can be applied to plants that utilize biomass as afuel source. In one embodiment, implementation of the present inventioncan be accomplished in a cost-effective manner utilizing low costhardware designed to supply the necessary iron compound to a combustionprocess. The present invention also does not affect the current designof boilers and SCRs.

In one embodiment, the amount of iron compound, or compounds, utilizedin conjunction with the present invention varies depending upon thephosphorus content in the coal to be burned. In one embodiment, thepresent invention is directed to a method and system whereby astoichiometric excess one or more iron compounds are supplied to anypoint prior to an SCR. While not wishing to be bound to any one theory,it has been found that by supplying a stoichiometric excess of ironupstream of an SCR, the catalytic activity and/or catalytic lifespan ofan SCR catalyst can be unexpectedly increased. As can be seen from thegraph of FIG. 2, the addition of a stoichiometric excess of one or moreiron-based compounds not only protects the SCR catalyst from poisoningvia various phosphorus compounds but also increases both the catalyticactivity and catalytic lifespan over a period of at least about 2,000operational hours.

Regarding FIG. 2, FIG. 2 is a graph plotting the original expecteddeactivation for a catalyst without the addition of the iron-bearingcompound, or compounds, of the present invention versus the actualdeactivation of a catalyst with the addition of an iron-bearing compoundof the present invention versus the observed deactivation of a catalystwithout the addition of the iron-bearing compound, or compounds, of thepresent invention. The y-axis of the graph of FIG. 2 is catalyticactivity in decimal terms where 0.9 is equivalent to 90 percent activityas measured when compared to unused virgin catalyst as determined usingany suitable method for determining catalytic activity known to those ofskill in the art. The x-axis of the graph of FIG. 2 is the number ofoperational hours that the catalyst in question is exposed to theaverage operational conditions of a 100 MWe coal plant.

Given the above, in one embodiment the present invention achieves eitherone, or both, of an increase in catalytic activity and/or an increase incatalytic lifespan via the use, introduction and/or delivery of one ormore iron-based compounds. In one embodiment, an increase in either one,or both, of catalytic activity and/or catalytic lifespan of at leastabout 10 percent is achieved at an operational time of at least about2,000 hours versus the catalytic activity and/or catalytic lifespan of agiven catalyst when subjected to similar operational conditions but notsubjected to a supply of one or more iron-based compounds as disclosedherein. As would be apparent to those of skill in the art, various knownmethods are available to measure the baseline catalytic activity as wellas the catalytic activity of various catalysts, including SCR catalysts.As such, a detailed discussion herein is omitted for the sake ofbrevity.

In another embodiment, the present invention achieves an increase ineither one, or both, of catalytic activity and/or catalytic lifespan ofat least about 10 percent is achieved at an operational time of about2,000 hours, an increase of at least about 12.5 percent is achieved atan operational time of about 2,000 hours, an increase of at least about15 percent is achieved at an operational time of about 2,000 hours, anincrease of at least about 17.5 percent is achieved at an operationaltime of about 2,000 hours, an increase of at least about 20 percent isachieved at an operational time of about 2,000 hours, an increase of atleast about 22.5 percent is achieved at an operational time of about2,000 hours, an increase of at least about 25 percent is achieved at anoperational time of about 2,000 hours, an increase of at least about27.5 percent is achieved at an operational time of about 2,000 hours, oreven an increase of at least about 30 percent is achieved at anoperational time of about 2,000 hours versus the catalytic activityand/or catalytic lifespan of a given catalyst when subjected to similaroperational conditions but not subjected to a supply of one or moreiron-based compounds as disclosed herein. Here, as well as elsewhere inthe specification and claims, individual numerical values can becombined to form additional and/or non-disclosed ranges.

In still another embodiment, the present invention achieves an increasein either one, or both, of catalytic activity and/or catalytic lifespanof at least about 10 percent is achieved at an operational time of about2,500 hours, an increase of at least about 12.5 percent is achieved atan operational time of about 2,500 hours, an increase of at least about15 percent is achieved at an operational time of about 2,500 hours, anincrease of at least about 17.5 percent is achieved at an operationaltime of about 2,500 hours, an increase of at least about 20 percent isachieved at an operational time of about 2,500 hours, an increase of atleast about 22.5 percent is achieved at an operational time of about2,500 hours, an increase of at least about 25 percent is achieved at anoperational time of about 2,500 hours, an increase of at least about27.5 percent is achieved at an operational time of about 2,500 hours, oreven an increase of at least about 30 percent is achieved at anoperational time of about 2,500 hours versus the catalytic activityand/or catalytic lifespan of a given catalyst when subjected to similaroperational conditions but not subjected to a supply of one or moreiron-based compounds as disclosed herein. Here, as well as elsewhere inthe specification and claims, individual numerical values can becombined to form additional and/or non-disclosed ranges.

In still yet another embodiment, the present invention achieves anincrease in either one, or both, of catalytic activity and/or catalyticlifespan of at least about 10 percent, at least about 12.5 percent, atleast about 15 percent, at least about 17.5 percent, at least about 20percent, at least about 22.5 percent, at least about 25 percent, atleast about 27.5 percent, or even at least about 30 percent is achievedat an operational time of about 3,000 hours versus the catalyticactivity and/or catalytic lifespan of a given catalyst when subjected tosimilar operational conditions but not subjected to a supply of one ormore iron-based compounds as disclosed herein. In still yet anotherembodiment, the present invention achieves an increase in either one, orboth, of catalytic activity and/or catalytic lifespan of at least about10 percent, at least about 12.5 percent, at least about 15 percent, atleast about 17.5 percent, at least about 20 percent, at least about 22.5percent, at least about 25 percent, at least about 27.5 percent, or evenat least about 30 percent is achieved at an operational time of about3,500 hours, about 4,000 hours, about 4,500 hours, about 5,000 hours,about 6,000 hours, about 7,000 hours, about 7,500 hours, about 8,000hours, about 9,000 hours, about 10,000 hours, about 11,000 hours, about12,000 hours, about 13,000 hours, about 14,000 hours, about 15,000hours, or even about 16,000 hours versus the catalytic activity and/orcatalytic lifespan of a given catalyst when subjected to similaroperational conditions but not subjected to a supply of one or moreiron-based compounds as disclosed herein. Here, as well as elsewhere inthe specification and claims, individual numerical values can becombined to form additional and/or non-disclosed ranges.

As is known to those of skill in the art, the phosphorus content of coalcan be determined by various known methods. Thus, in this instance, thepresent invention is not limited to any one range of iron compounds thatare utilized. Instead, an excess stoichiometric ratio is utilized. Inone embodiment, the excess stoichiometric ratio of iron to phosphorus isin the range of about 2.5:1 to about 10:1, or from about 3:1 to about9:1, or from about 3.5:1 to about 8:1, or from about 4:1 to about 7.5:1,or from about 5:1 to about 7:1, or from about 5.5:1 to about 6.5:1, oreven about 6:1. Here, as well as elsewhere in the specification andclaims, individual range values can be combined to form additionaland/or non-disclosed ranges.

In another embodiment, the amount of iron compound, or compounds,utilized in conjunction with the present invention is within a givenrange when the coal utilized is Powder River Basin/Lignite coal. In thisembodiment, the amount of the iron compound, or compounds, to PowderRiver Basin/Lignite coal is expressed as the amount of iron compound, orcompounds, (hereinafter referred to as just “iron” in only thisinstance) in pounds for every 1,000 pounds of coal. In one embodiment,the amount of iron compound, or compounds, utilized is in the range ofabout 5 pounds of “iron” per 1,000 pounds of coal to about 20 pounds of“iron” per 1,000 pounds of coal. In another embodiment, the amount ofiron compound, or compounds, utilized is in the range of about 5.5pounds of “iron” per 1,000 pounds of coal to about 17.5 pounds of “iron”per 1,000 pounds of coal, or from about 6 pounds of “iron” per 1,000pounds of coal to about 15 pounds of “iron” per 1,000 pounds of coal, orfrom about 7 pounds of “iron” per 1,000 pounds of coal to about 12.5pounds of “iron” per 1,000 pounds of coal, or from about 7.5 pounds of“iron” per 1,000 pounds of coal to about 10 pounds of “iron” per 1,000pounds of coal, or even from about 8 pounds of “iron” per 1,000 poundsof coal to about 9 pounds of “iron” per 1,000 pounds of coal. Here, aswell as elsewhere in the specification and claims, individual rangevalues can be combined to form additional and/or non-disclosed ranges.

In another embodiment, where both an iron-based compound and a halidecompound as defined above are utilized, the amount of iron-basedcompound, or compounds, as compared on a weight basis to the amount ofone or more halide compounds is in the range of about 95 weight partsiron based compound, or compounds to about 5 weight parts halidecompound, or compounds. In another embodiment, the weight ratio ofiron-based compound, or compounds, to halide compound, or compounds, isin the range of about 95:5 to about 75:25, or from about 93.5:6.5 toabout 80:20, or from about 92:8 to about 82.5:17.5, or from about 91:9to about 85:15, or even from about 90:10 to about 87.5:12.5. Thus, inone embodiment, the amount of the one or more halide compounds, if soutilized, can be calculated based on any of the above stated iron-basedcompound, or compounds, amounts via the ratios disclosed in thisparagraph. Here, as well as elsewhere in the specification and claims,individual range values can be combined to form additional and/ornon-disclosed ranges.

In another embodiment, the injection rate of the one or more halidecompounds, if so utilized in conjunction with the present invention, forcontrolling mercury in a flue gas, or combustion gas, is based on anon-limiting example of a 100 MWe coal power plant. In this case, theinjection rate for the one or more halide compounds, if in solution, isin the range of about 0.25 gallons per hour to about 10 gallons perhour, or from about 0.5 gallons per hour to about 5 gallons per hour, oreven from about 1 gallon per hour to about 4 gallons per hour. Inanother embodiment, regardless of power plant or combustion plant size,the one or more halide compounds are supplied at any rate to a flue gas,or combustion gas, sufficient to yield a concentration of halide (e.g.,bromide, chloride or iodide) between about 10 ppm to about 200 ppm, orfrom about 25 ppm to about 175 ppm, or from about 50 ppm to about 150ppm. It should be noted that depending upon the emissions controltechnology in place on the device generating the flue gas, or combustiongas, it may be desirable to use a lower halide concentration in order toprevent any type of detrimental effects to such downstream emissionstechnology. In one embodiment of such an instance the concentration ofhalide is between about 10 ppm to about 125 ppm, or from about 25 ppm toabout 100 ppm, or from about 50 ppm to about 75 ppm. Here, as well aselsewhere in the specification and claims, individual range values (evenfrom different embodiments) can be combined to form additional and/ornon-disclosed ranges.

In light of the above, one of skill in the art would recognize that theamount of one or more iron, or iron-based, compounds necessary to supplythe desired amount of iron to a flue gas, or combustion gas, inaccordance with the process of the present invention will vary dependingupon the size of the device generating such flue gas, or combustion gas.The same can be said of the one or more halide compounds. That is, oneof skill in the art would recognize that the amount of one or morehalide compounds necessary to supply the desired amount of halide to aflue gas, or combustion gas, in accordance with the process of thepresent invention will vary depending upon the size of the devicegenerating such flue gas, or combustion gas. Thus, the present inventionis not limited to any specific rate or range of supply.

In another embodiment, for a 100 MWe coal power plant the amount ofhalide solution (25 weight percent solution) supplied to the flue gas,or combustion gas, is in the range of about 0.25 gallons per hour toabout 6 gallons per hour, or from 0.5 gallons per hour to about 5gallons per hour, or even from 1 gallon per hour to about 4 gallons perhour. Here, as well as elsewhere in the specification and claims,individual range values can be combined to form additional and/ornon-disclosed ranges. However, as is noted above, the present inventionis not limited to solely these supply rates. Rather, any supply rate canbe used in order to achieve the desired concentration of halide.

As would be apparent to one of skill in the art, other additionalfactors can impact the amount of iron-based, iron-bearing and/or ironcompounds supplied in connection with the various embodiments of thepresent invention. Such additional factors include, but are not limitedto, the amount and/or type of phosphorus present in the coal, or othercombustible fuel; the size and/or output of the boiler, heater, kiln, orother flue gas-, or combustion gas-, generating device; and the desiredstoichiometric ratio to be achieved; the type and/or manner ofcombustion, the type and/or arrangement of any applicable equipment orstructure.

In another embodiment, the one or more iron compounds and/or the one ormore halide compounds utilized in conjunction with the present inventioncan be of any particle size and/or particle geometry. Suitable particlegeometries include, but are not limited to, spherical, platelet-like,irregular, elliptical, oblong, or a combination of two or more differentparticle geometries. As would be apparent to those of skill in the art,each different compound, or even the same compound, can be supplied inthe form of one or more particle geometries. In one embodiment, the oneor more iron compounds and/or the one or more halide compounds of thepresent invention, if water soluble, can be supplied in solution form,either independently or together so long as the active components to bedelivered to the flue, or combustion, gas do not adversely react. Insuch an instance, a solution concentration of at least about 15 weightpercent of one or more water soluble iron compounds and/or one or morewater soluble halide compounds is utilized. In another embodiment, asolution concentration of at least about 20 weight percent, at leastabout 25 weight percent, at least about 30 weight percent, at leastabout 35 weight percent, at least about 40 weight percent, at leastabout 45 weight percent, or even at least about 50 weight percent ofmore of the one or more water soluble iron compounds and/or the one ormore water soluble halide compounds is utilized in conjunction with thepresent invention. Here, as well as elsewhere in the specification andclaims, individual range values can be combined to form additionaland/or non-disclosed ranges. As would be appreciated by those of skillin the art, the solution concentration of any one or more water solubleiron compounds and/or the one or more water soluble halide compoundsshould not, in one embodiment, exceed the solubility amount,respectively, for the one or more iron compounds and/or the one or morehalide compounds.

In still another embodiment, the one or more iron compounds and/or theone or more halide compounds of the present invention can be supplied ina powdered form, a solution form, an aqueous suspension form, or acombination of two or more thereof. In the case of an aqueoussuspension, the one or more iron compounds and/or the one or more halidecompounds utilized in conjunction with the present invention should havea suitable particle size. Additionally, even absent the desire to placethe one or more iron compounds and/or the one or more halide compoundsof the present invention into an aqueous solution, the one or more ironcompounds and/or the one or more halide compounds should have a suitableparticle size that facilitates a higher degree of reactivity when placedinto contact with a flue, or combustion, gas. In one embodiment, both ofthese conditions can be met, whether individually or in combination, byone or more iron compounds and/or one or more halide compounds where atleast about 95 percent of the particles have a particle size of lessthan about 400 μm (microns), where at least about 95 percent of theparticles have a particle size of less than about 350 μm (microns),where at least about 95 percent of the particles have a particle size ofless than about 300 μm (microns), where at least about 95 percent of theparticles have a particle size of less than about 250 μm (microns),where at least about 95 percent of the particles have a particle size ofless than about 200 μm (microns), or even where at least about 95percent of the particles have a particle size of less than about 175 μm(microns). Here, as well as elsewhere in the specification and claims,individual range values can be combined to form additional and/ornon-disclosed ranges.

Although not limited hereto, a suitable iron compound for use inconjunction with the present invention is iron (II) carbonate availablefrom Prince Agri Products (a subsidiary of Phibro Animal HealthCorporation located in Ridgefield Park, N.J.). This iron (II) carbonateis a powdered compound where at least about 95 percent of its particlesare less than 200 μm (microns) in size. Additionally, the concentrationof iron (II) carbonate in this product is about 80 percent by weightwith substantially all of the remaining 20 weight percent beingnon-reactive in light of the use here. A suitable halide compound foruse, if so desired, in conjunction with the present invention is calciumbromide available from Tetra Chemical (located in The Woodlands, Tex.).

In the instance where one or more aqueous suspensions is/are utilized inconjunction with the present invention, such aqueous suspension(s) canfurther comprise a suitable amount of one or more anti-settling,suspension, thickening or emulsification agents. Suitable anti-settling,suspension, thickening or emulsification agents include, but are notlimited to, sodium polyacrylates, carbomers, acrylates, and inorganicthickening agents. Other suitable anti-settling, suspension, thickeningor emulsification agents are known to those of skill in the art and assuch a discussion herein is omitted for the sake of brevity. In anotherembodiment, a suitable suspension or emulsification can be achieved viaagitation and does not necessarily require the use of one or moreanti-settling, suspension, thickening or emulsification agents. Inanother embodiment, a combination of one or more anti-settling,suspension, thickening or emulsification agents can be utilized incombination with agitation.

In still another embodiment, the one or more iron compounds and/or theone or more halide compounds of the present invention shouldindependently have a purity of at least about 50 weight percent, atleast about 55 weight percent, at least about 60 weight percent, atleast about 65 weight percent, at least about 70 weight percent, atleast about 75 weight percent, at least about 80 weight percent, atleast about 85 weight percent, at least about 90 weight percent, atleast about 95 weight percent, or even at least about 99 weight percentor higher. Here, as well as elsewhere in the specification and claims,individual range values can be combined to form additional and/ornon-disclosed ranges.

As for the portion of the one or more iron compounds that is not “aniron compound,” such impurities should be non-reactive in theenvironments present in conjunction with the present invention.Alternatively, if reactive, such impurities should either be easilycaptured, removed and/or sequestered, or should not add significantly toany further contamination of any catalyst downstream. In still anotherembodiment, the amount of phosphorus-containing compound impurities inany of the one or more iron compounds and/or the one or more halidecompounds that are utilized in conjunction with the present inventionshould independently be less than about 5 weight percent, less thanabout 2.5 weight percent, less than about 1 weight percent, less thanabout 0.5 weight percent, less than about 0.25 weight percent, less thanabout 0.1 weight percent, or even less than about 0.01 weight percent.Here, as well as elsewhere in the specification and claims, individualrange values can be combined to form additional and/or non-disclosedranges. In still yet another embodiment, the amount ofphosphorus-containing compound impurities in any of the one or more ironcompounds and/or the one or more halide compounds that are utilized inconjunction with the present invention should be zero. That is, in thisembodiment the one or more iron compounds and/or the one or more halidecompounds that are utilized in conjunction with the present inventionshould independently be free from any phosphorus-containing compounds.

While not wishing to be bound to any one theory, it is believed that thepresent invention exploits various preferential reactions betweenphosphorus compounds, or phosphorus-containing compounds, to sequestervarious phosphorus compounds, or phosphorus-containing compounds thatare detrimental to an increased active, or service, life of an SCRcatalyst. Thus, the reactions discussed herein are to be construed asnon-limiting in that other additional reactions may be occurring in thecombustion and/or flue gas stream.

In another embodiment, the present invention is direct to a system andmethod for the injection of iron carbonate, another suitable ironcompound, or a blend of one or more iron compounds and one or morenon-iron-containing halide compounds with coal in the furnace in orderto replenish the active catalytic sites on the surface of SCR catalystwith Fe active sites while simultaneously achieving mercury oxidation.In one instance, the injection material is a blend of iron carbonate(about 90 percent by weight) and a non-iron-containing halogen compound(e.g., calcium bromide 10 percent by weight). As is known to those ofskill in the art, any iron that is present in coal ash (including butnot limited to PRB coal ash) is not catalytically active as it bonds, oris bonded, with various silicates and/or aluminates in the coalcombustion process. In PRB coal more than 90 percent of total ironoccurs as a bonded mineral meaning that it is mostly trapped in glassysilica and/or alumina compounds during the combustion process therebymaking it unavailable for any other chemical reaction. Thus, the presentinvention, by injecting iron separately, provides “free” iron that,while not wishing to be bound to any one theory, is believed to settleonto and/or be deposited onto the surface of fly ash which makes itavailable for further chemical reactions.

This blended material that contains “free” iron as defined above canthen provide iron for increasing the catalytic activity and/or catalyticlifespan of the DeNO_(x) catalyst while, if so provided, the halogenportion of the one or more halide compounds of the present inventionacts to aid, or achieve, mercury oxidation. While not wishing to bebound to any one theory, is believed that when the fly ash getsdeposited on the surface of SCR catalyst the iron on the surface of flyash or iron deposited on catalyst as a result of the injection processprovides sites onto which ammonia and NO_(x) can react to form N₂ andwater. As the iron is injected continuously at a low rate of injection,any active iron sites that become depleted are replaced by new ironsites at a reasonable rate thereby allowing for the extension and/orincrease of catalytic lifespan and/or catalytic activity when comparedto similar untreated catalyst as explained in detail above. The halogenportion of the halide compound, or compounds, oxidizes elemental mercuryinto its oxidized form and make it easier for removal by a downstreamwet or dry scrubber, or with PAC injection.

While not wishing to be bound to any one example, data to support thisinvention is supplied from a long-term injection test of iron carbonateat a 100 MWe coal power plant. Before exposure of the catalyst to thecombustion flue gas, the catalyst analysis by XRF technique showednegligible iron present both on the surface and in the bulk of catalyst.After approximately 2,000 hours of operation and injection of FeCO₃ acatalyst sample is obtained and analyzed by XRF. This sample shows 0.35percent Fe on the surface and 0.13 percent Fe in bulk. Previously usedcatalyst (no FeCO₃ injection from the same site) had 0.26 percent Fe onsurface and 0.06 percent Fe in bulk after 11,000 hours of operation.Baseline testing prior to the injection of iron carbonate indicates thatthe SO₃ concentration is less than 1 ppm in flue gas at the outlet ofair heater. After 8,000 plus hours of operation the SO₃ concentration ismeasured at the air heater outlet and is about 2.6 ppm. This proves thatiron injection into the furnace is indeed reaching the SCR. The increasein SO₃ concentration can be related to the presence of iron on catalystsurface, since Fe is also a good catalyst for conversion of SO₂ to SO₃.

As noted above, FIG. 2 illustrates catalyst performance with and withoutiron injection. The upper line plot (the one with the lower case “Xs”)is the originally expected catalyst deactivation curve. This catalyst isexpected to last for about 16,000 hours of operation. The lower plot(diamonds) illustrates the actual performance for this catalyst. Thecatalyst actually lasts for only 6,800 hours of operation due tophosphorus deactivation. The middle line (triangles) illustrates theperformance of a catalyst subjected to at least the iron compoundinjection of the present invention. The catalyst in this example is notnew when it is installed but is regenerated catalyst with 15 percentlower initial activity than virgin catalyst.

Thus, in one embodiment, the present invention provides additional sitesfor the DeNO_(x) reaction by injection of one or more iron-bearingcompounds thereby making it possible to significantly improve the lifeand/or catalytic activity of an SCR catalyst beyond presently accepted,or believed, time spans. When utilized, the one or more halide compoundsof the present invention provide a halogen component that permits forincreased mercury oxidation and makes possible mercury removaldownstream by any suitable technology (e.g., AQCS equipment).

While specific embodiments of the present invention have been shown anddescribed in detail to illustrate the application and principles of theinvention, it will be understood that it is not intended that thepresent invention be limited thereto and that the invention may beembodied otherwise without departing from such principles. In someembodiments of the invention, certain features of the invention maysometimes be used to advantage without a corresponding use of the otherfeatures. Accordingly, all such changes and embodiments properly fallwithin the scope of the following claims.

What is claimed is:
 1. A method for increasing the active life of an SCRcatalyst, the method comprising the steps of: (a) providing a fuel to afurnace, or boiler, wherein the fuel is selected from a mixture of coaland biomass, a mixture of coal and bone meal, or biomass; (b) subjectingthe fuel to a combustion process, wherein the combustion processproduces at least one gaseous phosphorus compound and/or at least onegaseous phosphorus-containing compound; (c) providing at least oneiron-bearing compound to a combustion zone or flue gas stream of thefurnace, or boiler, prior to entry of the flue gas into an SCR, whereinthe SCR is located upstream of at least one air heater; and (d)permitting the at least one iron-bearing compound to react with the atleast one gaseous phosphorus compound and/or the at least one gaseousphosphorus-containing compound present in the combustion zone or fluegas prior to the entry of the flue gas into the SCR to form an ironphosphorus-containing compound.
 2. The method of claim 1, wherein the atleast one iron-bearing compound is selected from metallic iron, one ormore iron oxides, iron carbonate, or mixtures of two or more thereof. 3.The method of claim 1, wherein the at least one iron-bearing compound isselected from iron (III) oxide, iron (II) carbonate, iron (II) oxide, ormixtures of two or more thereof.
 4. The method of claim 1, wherein theat least one iron-bearing compound is selected from iron (III) oxide,iron (II) carbonate, or a mixture thereof.
 5. The method of claim 1,wherein the at least one iron-bearing compound is provided to thecombustion zone via addition to the coal portion of either the mixtureof coal and biomass or the mixture of coal and bone meal.
 6. The methodof claim 1, wherein the at least one iron-bearing compound is providedto the combustion zone via addition to the biomass portion of themixture of coal and biomass.
 7. The method of claim 1, wherein the atleast one iron-bearing compound is provided to the combustion zone viaaddition to the bone meal portion of the mixture of coal and bone meal.8. The method of claim 1, wherein the at least one iron-bearing compoundis provided to the combustion zone via addition to the biomass.
 9. Themethod of claim 1, wherein the at least one iron-bearing compound isprovided to the combustion zone via a dedicated supply line.
 10. Themethod of claim 1, wherein the at least one iron-bearing compound is awater soluble iron-bearing compound.
 11. The method of claim 1, whereinthe at least one iron-bearing compound is a water soluble iron-bearingcompound that is supplied in the form of an aqueous solution.
 12. Themethod of claim 1, wherein the at least one iron-bearing compound is awater insoluble iron-bearing compound that is supplied in the form of anaqueous suspension or emulsion.
 13. The method of claim 1, wherein theat least one iron-bearing compound is at least one iron-bearing halide,and wherein Step (d) involves: permitting the iron portion of the atleast one iron-bearing halide compound to react with the at least onegaseous phosphorus compound and/or the at least one gaseousphosphorus-containing compound present in the combustion zone or fluegas prior to the entry of the flue gas into the SCR to form an ironphosphorus-containing compound; and wherein the method further includesthe step of: (e) permitting the halide portion of the at least oneiron-bearing halide compound to react with any gaseous mercurycompounds, or mercury-containing compounds, present in the combustionzone or flue gas.
 14. The method of claim 13, wherein the at least oneiron-bearing halide compound is selected from iron (II) bromide, iron(III) bromide, iron (II) chloride, iron (III) chloride, iron (II)iodide, iron (III) iodate, or mixtures of two or more thereof.
 15. Themethod of claim 13, wherein the at least one iron-bearing halidecompound is iron (II) bromide.
 16. The method of claim 13, wherein theat least one iron-bearing halide compound is provided at sufficientamount to yield a halide concentration of between about 10 ppm to about200 ppm.
 17. A method for sequestering one or more gaseous phosphoruscompounds, or gaseous phosphorus-containing compounds, in the form ofone or more less reactive iron-phosphorus-containing compounds, themethod comprising the steps of: (i) providing a fuel to a furnace, orboiler, wherein the fuel is selected from a mixture of coal and biomass,a mixture of coal and bone meal, or biomass; (ii) subjecting the fuel toa combustion process, wherein the combustion process produces at leastone gaseous phosphorus compound and/or at least one gaseousphosphorus-containing compound; (iii) providing at least oneiron-bearing compound to a combustion zone or flue gas stream of thefurnace, or boiler; and (iv) permitting the at least one iron-bearingcompound to react with the at least one gaseous phosphorus compoundand/or the at least one gaseous phosphorus-containing compound presentin the combustion zone or flue gas to form one or more less reactiveiron-phosphorus-containing compounds.
 18. The method of claim 17,wherein the at least one iron-bearing compound is selected from metalliciron, one or more iron oxides, iron carbonate, or mixtures of two ormore thereof.
 19. The method of claim 17, wherein the at least oneiron-bearing compound is selected from iron (III) oxide, iron (II)carbonate, iron (II) oxide, or mixtures of two or more thereof.
 20. Themethod of claim 17, wherein the at least one iron-bearing compound isselected from iron (III) oxide, iron (II) carbonate, or a mixturethereof.
 21. The method of claim 17, wherein the at least oneiron-bearing compound is provided to the combustion zone via addition tothe coal portion of either the mixture of coal and biomass or themixture of coal and bone meal.
 22. The method of claim 17, wherein theat least one iron-bearing compound is provided to the combustion zonevia addition to the biomass portion of the mixture of coal and biomass.23. The method of claim 17, wherein the at least one iron-bearingcompound is provided to the combustion zone via addition to the bonemeal portion of the mixture of coal and bone meal.
 24. The method ofclaim 17, wherein the at least one iron-bearing compound is provided tothe combustion zone via addition to the biomass.
 25. The method of claim17, wherein the at least one iron-bearing compound is provided to thecombustion zone via a dedicated supply line.
 26. The method of claim 17,wherein the at least one iron-bearing compound is a water solubleiron-bearing compound.
 27. The method of claim 17, wherein the at leastone iron-bearing compound is a water soluble iron-bearing compound thatis supplied in the form of an aqueous solution.
 28. The method of claim17, wherein the at least one iron-bearing compound is a water insolubleiron-bearing compound that is supplied in the form of an aqueoussuspension or emulsion.
 29. The method of claim 17, wherein the at leastone iron-bearing compound is at least one iron-bearing halide, andwherein Step (iv) involves: permitting the iron portion of the at leastone iron-bearing halide compound to react with the at least one gaseousphosphorus compound and/or the at least one gaseousphosphorus-containing compound present in the combustion zone or fluegas to form an iron phosphorus-containing compound; and wherein themethod further includes the step of: (v) permitting the halide portionof the at least one iron-bearing halide compound to react with anygaseous mercury compounds, or mercury-containing compounds, present inthe combustion zone or flue gas.
 30. The method of claim 29, wherein theat least one iron-bearing halide compound is selected from iron (II)bromide, iron (III) bromide, iron (II) chloride, iron (III) chloride,iron (II) iodide, iron (III) iodate, or mixtures of two or more thereof.31. The method of claim 29, wherein the at least one iron-bearing halidecompound is iron (II) bromide.
 32. The method of claim 29, wherein theat least one iron-bearing halide-bearing compound is provided atsufficient amount to yield a halide concentration of between about 10ppm to about 200 ppm.
 33. A method for increasing the active life of anSCR catalyst, the method comprising the steps of: (A) providing a fuelto a furnace, or boiler, wherein the fuel is selected from a mixture ofcoal and biomass, a mixture of coal and bone meal, or biomass; (B)subjecting the fuel to a combustion process, wherein the combustionprocess produces at least one gaseous phosphorus compound and/or atleast one gaseous phosphorus-containing compound; (C) providing at leastone iron-bearing compound to a combustion zone or flue gas stream of thefurnace, or boiler, prior to entry of the flue gas into an SCR, whereinthe SCR is located upstream of at least one air heater; and (D)permitting the at least one iron-bearing compound to react with the atleast one gaseous phosphorus compound and/or the at least one gaseousphosphorus-containing compound present in the combustion zone or fluegas prior to the entry of the flue gas into the SCR to form an ironphosphorus-containing compound, wherein the method achieves an increasein either one, or both, of a catalytic activity and/or a catalyticlifespan of at least about 10 percent at an operational time of at leastabout 4,000 hours.
 34. The method of claim 33, wherein the at least oneiron-bearing compound is selected from metallic iron, one or more ironoxides, iron carbonate, or mixtures of two or more thereof.
 35. Themethod of claim 33, wherein the at least one iron-bearing compound isselected from iron (III) oxide, iron (II) carbonate, iron (II) oxide, ormixtures of two or more thereof.
 36. The method of claim 33, wherein theat least one iron-bearing compound is selected from iron (III) oxide,iron (II) carbonate, or a mixture thereof.
 37. The method of claim 33,wherein the at least one iron-bearing compound is provided to thecombustion zone via addition to the coal portion of either the mixtureof coal and biomass or the mixture of coal and bone meal.
 38. The methodof claim 33, wherein the at least one iron-bearing compound is providedto the combustion zone via addition to the biomass portion of themixture of coal and biomass.
 39. The method of claim 33, wherein the atleast one iron-bearing compound is provided to the combustion zone viaaddition to the bone meal portion of the mixture of coal and bone meal.40. The method of claim 33, wherein the at least one iron-bearingcompound is provided to the combustion zone via addition to the biomass.41. The method of claim 33, wherein the at least one iron-bearingcompound is provided to the combustion zone via a dedicated supply line.42. The method of claim 33, wherein the at least one iron-bearingcompound is a water soluble iron-bearing compound.
 43. The method ofclaim 33, wherein the at least one iron-bearing compound is a watersoluble iron-bearing compound that is supplied in the form of an aqueoussolution.
 44. The method of claim 33, wherein the at least oneiron-bearing compound is a water insoluble iron-bearing compound that issupplied in the form of an aqueous suspension or emulsion.
 45. Themethod of claim 33, wherein the method further includes the step of: (E)providing at least one halide-bearing compound to a combustion zone orflue gas stream of a furnace, or boiler, prior to entry of the flue gasinto an SCR, with the proviso that halide-bearing compound is not aniron halide; and (F) permitting the at least one halide-bearing compoundto react with and/or oxidize any mercury present in the combustion zoneor flue gas,
 46. The method of claim 45, wherein the at least onehalide-bearing compound is selected from potassium bromide, potassiumchloride, potassium fluoride, potassium iodide, sodium bromide, sodiumchloride, sodium fluoride, sodium iodide, calcium bromide, calciumchloride, calcium fluoride, calcium iodide, aluminum bromide, aluminumchloride, aluminum fluoride, aluminum iodide, transition metal halideswith the proviso that the transition metal is not iron, or any mixtureof two or more thereof or mixtures of two or more thereof.
 47. Themethod of claim 45, wherein the at least one iron-bearing compound isselected from iron (II) carbonate and the at least one halide-bearingcompound is selected from calcium bromide.
 48. The method of claim 45,wherein the at least one halide-bearing compound is provided atsufficient amount to yield a halide concentration of between about 10ppm to about 200 ppm.
 49. A method for increasing the active life of anSCR catalyst, the method comprising the steps of: (I) providing a fuelto a furnace, or boiler, wherein the fuel is selected from a mixture ofcoal and biomass, a mixture of coal and bone meal, or biomass; (II)subjecting the fuel to a combustion process, wherein the combustionprocess produces at least one gaseous phosphorus compound and/or atleast one gaseous phosphorus-containing compound; (III) providing atleast one iron-bearing compound to a combustion zone or flue gas streamof the furnace, or boiler, prior to entry of the flue gas into an SCR,wherein the SCR is located upstream of at least one air heater; (IV)permitting the at least one iron-bearing compound to react with the atleast one gaseous phosphorus compound and/or the at least one gaseousphosphorus-containing compound present in the combustion zone or fluegas prior to the entry of the flue gas into the SCR to form an ironphosphorus-containing compound; (V) providing at least onehalide-bearing compound to a combustion zone or flue gas stream of afurnace, or boiler, prior to entry of the flue gas into an SCR, with theproviso that halide-bearing compound is not an iron halide; and (VI)permitting the at least one halide-bearing compound to react with and/oroxidize any mercury present in the combustion zone or flue gas.
 50. Themethod of claim 49, wherein the at least one iron-bearing compound isselected from metallic iron, one or more iron oxides, iron carbonate, ormixtures of two or more thereof.
 51. The method of claim 49, wherein theat least one iron-bearing compound is selected from iron (III) oxide,iron (II) carbonate, iron (II) oxide, or mixtures of two or morethereof.
 52. The method of claim 49, wherein the at least oneiron-bearing compound is selected from iron (III) oxide, iron (II)carbonate, or a mixture thereof.
 53. The method of claim 49, wherein theat least one halide-bearing compound is selected from potassium bromide,potassium chloride, potassium fluoride, potassium iodide, sodiumbromide, sodium chloride, sodium fluoride, sodium iodide, calciumbromide, calcium chloride, calcium fluoride, calcium iodide, aluminumbromide, aluminum chloride, aluminum fluoride, aluminum iodide,transition metal halides with the proviso that the transition metal isnot iron, or any mixture of two or more thereof or mixtures of two ormore thereof.
 54. The method of claim 49, wherein the at least oneiron-bearing compound is selected from iron (II) carbonate and the atleast one halide-bearing compound is selected from calcium bromide. 55.The method of claim 49, wherein the at least one iron-bearing compoundis a water soluble iron-bearing compound.
 56. The method of claim 49,wherein the at least one iron-bearing compound is a water solubleiron-bearing compound that is supplied in the form of an aqueoussolution.
 57. The method of claim 49, wherein the at least oneiron-bearing compound is a water insoluble iron-bearing compound that issupplied in the form of an aqueous suspension or emulsion.